Production of monocarboxylic acids



Patented June 26, 1934 ITED STATES PATENT OFFICE ACI Alphons O. Jaeger, Grafton, Pa., assignor to The Selden Company, tion of Delaware N 0 Drawing. Application Pittsburgh, Pa., a corpora- October 3, 1927,

Serial No. 223,845

3 Claims.

This invention relates to catalytic processes of producing monocarboxylic acids for polycarboxylic acids, and particularly from dicarboxylic acids.

In the past monocarboxylic acids have been produced from certain dicarboxylic acids and polycarboxylic acids by various methods, usually involving the heating of salts of the polycarboxylic acids. A typical example is the production of benzoic acid from phthalic acid by heating phthalic anhydride with caustic soda or lime to a high temperature. The processes are expensive, awkward, and frequently give poor yields and impure products. They are at present of little or no practical importance.

According to the present invention monocarboxylic acids are produced from polycarboxylic acids, and particularly from dicarboxylic acids in the vapor phase, by passing vapors of suitable polycarboxylic acids (those which can be practically volatilized), or some of their deriva tives, such as for example esters, halogen and sulfo derivatives and the like, over suitable catalysts at an elevated temperature, the class of cata lysts being that which favors the splitting on? of C02. The reaction can take place in the presence or absence of air, nitrogen or other indifferent gases, and may advantageously take place in the presence of steam, particularly when derivatives of the aids such as anhydrides are used. The process of the present invention is simple, continuous and cheap, and avoids the diiiiculties obtained in the processes of the prior art. When suitable reaction conditions and catalysts are chosen, good yields are obtained, and the products possess a high degree of purity.

Theoretically, the formation of monocarboxylic acids from polycarboxylic acids or from some of their derivatives, would not require the presence of any steam. When the anhydrides are used theoretically a small amount of steam would be required. Practically I have found that in most cases it is desirable to work with an excess of steam, particularly when dealing with anhydrides, as the presence of a moderate excess of steam appears to prevent, or at least to retard the decomposition of the monocarboxylic acids formed, or the complete break-up of the carbon chain generally to hydrogen, methane or other hydrocarbons. At the same time, particularly when carrying out the reaction at high temperature, the presence of steam in moderate excess appears to prevent to a large extent the formation of pyrogenetic products. The inven tion, however, when carried out with polycarsence of steam. The preferred method, however,

involves the utilization of a moderate excess of steam over that theoretically required.

The reaction can also be carried out in a continuous process, particularly when indifferent gases are used, the indifferent gases mixed with 6-3 the polycarboxylic acid together with any steam necessary being introduced at one point in the circulation and the monocarboxylic acid removed at another point. In such a process carbon dioxide which is produced may be removed by alkalies or washing with water under pressure, or part or all of it may be permitted to remain in the circulation as I have found that the presence of carbon dioxide does not exercise any deleterious effects on the process, and on the contrary in many cases is of advantage, as an excess of carbon dioxide appears to smooth out the splitting reaction and permit high yields of the monocarboxylic acids, frequently of greater purity. The process can be carried out at pressure, under a vacuum or at high pressures, and with many catalysts particularly zeolite catalysts it is desirable to use a moderate pressure. I have found that in most cases 3 to 5 atmospheres is suiiicient, but the invention is of limited to any particular pressure. Not only can carbon dioxide be permitted to remain in processes using a circulation of inert gases but it is sometimes desirable to add carbon dioxide from an outside source to the reaction gases either in 1 a circulatory process or even in a non-circulatory process, and this feature is included in the scope of the invention.

Instead of utilizing the polycarboxylic acids themselves or their anhydrides, and particularly dicarboxylic acids and their anhydrides, it is possible in some cases to combine the process of the present invention with the catalytic production of the polycarboxylic acids or their anhydrides, for example the catalytic production of products phthalic anhydride, maleic acid, naphthalic anhydride, diphenic acid and the like. In such cases the reaction mixtures containing the acids or their anhydrides may directly pass over suitable carbon dioxide splitting catalysts under the correct reaction conditions if necessary with the addition of steam. It is also practical to remove certain constituents of these reaction mixtures, for example by fractional condensation at high temperature to effect a partial purification, and such atmospheric 30 course not 5 processes are also included in the scope of the present invention. A typical example of a combined process is the direct production of benzoic acid from naphthalene by first oxidizing the naphthalene to phthalic anhydride, for example by passing a mixture of naphthalene and air over contact masses containing vanadium compounds or compounds of other suitable catalytic elements and then passing the mixture of reacted gases containing phthalic anhydride, if necessary with the addition of steam, over CO2 splitting catalysts at a suitable reaction temperature. In a similar manner other products can be prepared by a con-- bined oxidation and carbon dioxide splitting process. t should be noted that in some cases the production of the polycarboxylic acid or its anhydride may be accompanied by a considerable formation of water, particularly where the catalystlyst used may produce considerable total combustion. In many cases the water thus formed may be sufficient for the following process of splitting oil carbon dioxide, and of course replaces an equivalent amount of steam, which might normally have to be added to carry out the reaction.

In addition to the polycarboxylic acids referred to above, adipic acid, succinic acid, pyrotartaric acid, glutaric acid and the like may be transformed into the corresponding monocarboxylic acids, and in fact the reaction is generally applicable to all dicarboxylic acids and their derivatives which are volatile without decomposition.

Many substituted polycarboxylic acids, such as for example halogen and sulio-substituted phthalic anhydride, naphthalic anhydride, diphenic acid and the like may be subjected to the process of the present invention under suitable conditions. In some cases part or all of the substituent groups remain and corresponding substituted monocarboxylic acids are produced. In other cases some of the substituent carbons may also be split off during the reaction. Similarly, where other derivatives such as for example, esters are used, the alcoholic groups may all be split ofi during the reaction, yielding the corresponding monocarboxylic acid, or in some cases under suitable conditions only one of the ester groups is split off and an ester of the monocarboxylic acid is obtained.

The choice of the catalyst and reaction conditions will determine in most cases whether substantially all of the polycarboxylic acid is transformed into monocarboxylic acids or whether these latter are produced in admixture with some of the unchanged polycarboxylic acid.

The catalysts include metals, metal oxides, hydroxides, carbonates, salts, both simple and double, and other compounds used singly or in admixture, with or without diluents or carriers, such as pumice, quartz, quartz filter stones, fragments of earthenware, silicates, particularly materials rich in silicon, both natural and artificial. Among the effective catalytic components which favor the splitting off of carbondioxide and water are finely divided nickel, copper, iron. zinc, cadmium. FeO, F8203, A1203, TlOz, CuO, ZnO. CdO, NiO, C6203, ZlOz, N03, U308, SD02 CdCOz, ZIlCOs, CllCOs, NiCOs, ThOz, oxides of manganese, lead and the rare earths, carbonates of calcium, borium and lithium, calcium hydroxide, soda lime, double salts of thorium and alkaline earth metals and the like. These catalytic components may be present singly or in admixture.

Minerals can also be used, such as for example bog iron ore, bauxite, pyrolusite and the like.

Very effective contact mass compositions are those containing greater or less amounts of calcium hydroxide or carbonate, or a mixture of calcium and bariumcarbonates, a mixture of hydroxides or carbonates of calcium and alkali metals, in addition to the oxides and carbonates of the metals copper, nickel, iron, zinc, cadmium, cobalt, lead, aluminum and zirconium.

Basic metal salts, particularly tungstates, m0- lybdates, vanadates, chromates, tantalates, bismuthates, antimoniates, single or in admixtures, are also catalytically efiective for the splitting of carboxylic groups from polycarboxylic acids, in the vapor phase. But these salts are for the most part less active than the catalysts described above, require in general higher reaction temperatures, and tend to produce mixtures of polyand monocarboxylic acids.

Another very important class of catalysts, particularly those containing the catalytic components enumerated above, are base exchange bodies both zeolites and non-silicious, natural and artificial. These base exchange bodies may contain the catalytically active element in nonexchangeable form or as an exchangeable basand be both diluted or undiluted. In the former case the zeolite itself may be the catalyst, or the diluent may be catalytically active, or both. Salt-like bodies formed by the action of compounds containing suitable anions with zeolites are also effective in many cases for the reaction, and are included. It should be understood that the zeolites may be either two-component zeolites, that is to say, the reaction products either of metallates or of metal salts with soluble silicates, or they may be the so-called multi-cornponent zeolites, which are reaction products of at least one metallate, at least one metal salt and at least one soluble silicate, which products are described in my co-pending application, Serial No. 142,783, filed October 19, 1926.

I have found that very desirable catalysts or carriers can also be obtained by treating base exchange bodies with mineral acids to leach out the alkaline exchangeable bases and part or all of the metal elements present in non-exchangeable form. These are the so-called metallo silicic acids or cyclosilicic acids, and share some of the characteristics of zeolites and nonsilicious base exchange bodies, particularly their high and frequently submicronic porosity, which renders them so important as contact masses.

It is desirable in many cases to subject catalysts or contact masses such as those described above to the action of reducing gases at elevated r temperatures, such as for example hydrogen, water gas, illuminating gas, methane and the like, which in many cases reduces some or all of the metal compounds present to the metallic state, the metals being in an extraordinarily finely divided. state. Such catalysts are particularly efiective when the reduced metals are associated with alkaline earth compounds, such as for example calcium carbonate.

Example 1 6.55 parts of copper nitrate are dissolved in 50 parts of water and precipitated in the form of basic copper carbonate by means of a 2N sodium carbonate solution. The precipitate is sucked, lightly washed with water and then kneaded with 6 parts of calcium hydroxide with the gradual addition of parts of water. The suspension thus obtained is then coated on to 200 volumes of pea size pumice granules, preferably by heating the pumice and spraying the suspension on to it with agitation, the excess water being evaporated and a completely uniform coating of the pumice granules being effected.

The contact mass thus produced is well suited for the production of benzoic acid from phthalic anhydride by passing vapors of phthalic anhydride mixed with steam over the contact mass, which is maintained at a reaction temperature of 380-420 C. The proportion of water in the vapor form to phthalic anhydride in the vapor form can be varied within wide limits. I have found that a good proportion is one part of phthalic anhydride to ten parts of water.

The resulting reaction product consists essentially in benzoic acid contaminated with more or less phthalic acid, depending on the loading of the contact mass. A loading of four parts of phthalic anhydricle per hour per 160 volumes of contact mass at 400-420" C. gives yields of benzoic acid amounting to about 85 per cent or the theory.

The benzoic acid can be separated from the phthalic acid impurity by various means, for example by extraction with organic solvents such as benzol, ether, chloroform and others, preferably in the continuous process, the solvents extracting the benzoic acid but possessing practically no solvent power for phthalic acid. The mixture of benzoic acid and phthalic acid may also be evaporated, transforming the latter into phthalic anhydride, a separation then being efiFected by blowing steam at a temperature below 190 C. into the mixed vapors, benzoic acid being distilled over substantially uncontaminated, whereas phthalic anhydride is transformed into phthalic acid which possesses a far lower volatility and is therefore thrown down. In this manner a selective separation of the two products is obtained in the vapor phase. This process is not claimed as such in the present application apart from its use with the process of producing benzoic acid from phthalic anhydride, and on the contrary it forms part of the subject-matter of my co -pending Patent Number 1,686,913 dated Oct. 9, 1928. Of course instead of recovering the mixture of benzoic and phthalic acids after passing through the converter and then separating them, steam of suitable temperature can be blown into the gases, leaving the converter, effecting a separation in a continuous process.

When the reaction conditions are not kept perfect small amounts of benzol, diphenyl, benzophenone and anthraquinone are obtained in addition to benzoic acid, from which they can also easily be separated by the usual means.

Instead of using copper carbonate as the catalytically efiective component of this contact mass, copper oxide, nickel oxide or carbonate and the oxides or carbonates of iron, Zinc, cadmium, lead, aluminum, titanium, manganese and thorium may be used singly or in admixture. Calcium hydroxide may be substituted by barium hydro-xide or carbonate, soda lime, lithium carbonate or mixtures of the oxides and salts of the alkali and alkaline earth metals. Very efiective catalysts for the above process can also be obtained by treating the contact mass described with reducing gases such as hydrogen, water gas and the like, usually the treatment taking place at temperatures from 200 to 400 C. and resulting in the reduction of most of the copper compounds to finely divided copper.

The phthalic anhydride vapor-steam mixture may also be diluted or mixed with indifferent gases such as for example nitrogen, in which case the reaction product may frequently be obtained in solid form. The reaction gases mixed with the excess steam and indifierent gases after leaving the converter are cooled down suificiently to precipitate the monocarboxylic acids produced in solid form, the temperature, however, being kept suificiently high so that the excess steam and indifierent gases pass on and can be recirculated through the converter after the addition of the necessary components to re-establish the desired proportions of the reaction ingredients. Carbon dioxide can be permitted to accumulate, and then acts as part or all of the inert gas, or it may be removed from the mixture of steam and fixed inert gas by absorption in alkalies or solution in water under pressure. Air may also be mixed with the vapors of polycarboxylic acid, such as phthalic anhydride and steam, in which case preferably a greater excess of steam is to be used than when the diluting gas is completely indifferent, as is nitrogen, since under the reaction conditions a catalytic oxidation process might start with some of the catalysts in the presence of the oxygen of the air, which reaction is partly or wholly prevented by suificient excess steam.

Example 2 Contact masses are prepared as described in Example 1, and a mixture of vapors of maleic acid and steam are passed over the catalyst at 320-380= C. Acrylic acid is obtained as the main reaction product. The process may also be carried out as a circulatory process, using an indifferent gas, or using air, as described in connection with the production of benzoic acid in Example 1, the reaction conditions of course being adjusted for the splitting oil of carbon dioxide from maieic acid instead of phthalic.

Example 3 (l) A solution of 30-36 B. potassium waterglass diluted with 10 to 12 volumes of Water and containing 48 to 96 parts of SiOz is treated with sufiicient 20 per cent ammonia water until the cloudiness which has formed clears up.

(2) 29 parts of copper nitrate plus 61-120 are dissolved in water to form a N /l0 solution, and sufiicient strong ammonia water is added until the precipitate which first forms dissolves up again to form a deep blue cuprammonium compound, which is then poured into solution (1) with vigorous stirring.

A 10 per cent aluminum nitrate solution is prepared and is gradually added to the mixture of waterglass and cuprammonium nitrate solution until the reaction mixture is just neutral to phenolphthalein. The reaction product consists of a deep blue gel, which is pressed and dried, when it forms greenish-blue fragments of conchoidal fracture, which disintegrate into small pieces when placed in hot water. The cuprammonium complex can be replaced partly or wholly by nickel complexes, and the aluminum nitrate may also be replaced partly or wholly by other metal salt solutions, such as those containing copper, nickel, iron, manganese, cobalt, silver, lead or zinc, singly or in admixture.

The contact masses thus produced consist of three component zeolites, and are treated with sufficient 5 per cent calcium chloride solution to replace the exchangeable alkali by calcium. This can preferably be efiected by trickling the calcium chloride solution over the base exchange body. It is also advantageous to first trickle water over the base exchange body before attempting base exchange. The products thus obtained are effective catalysts for the splitting off of one or more carboxylic groups from polycarboxylic acids to form monocarboxylic acids. Thus for example, naphthalic anhydride vapors mixed with a great excess of steam are passed over the catalyst at 360420 C. and produce naphthalic acid contaminated with some naphthalene and naphthalic anhydride.

Instead of using naphthalic anhydride vapors phthalic anhydride vapors may be used under similar reaction conditions when high percentage yields of benzoic acid are obtained. Similarly phenylbenzoic acid can be produced from diphenic acid, acrylic acid from maleic acid, propionic acid from succinic acid, butyric acid from pyrotartaric acid, and the various chlor-benzoic acids from the corresponding chlor-phthalic acids. Benzoic acid and methylbenzoate may also be obtained from dimethylphthalate. The resulting acids are of greater or less purity, and can be purified by various means, mostly Well known.

The zeolites described above can advantageously be diluted without substantial loss of efficiency by introducing keiselguhr, pumice meal, ground quartz or the like, into the zeolites particularly during formation.

The contact masses diluted or undiluted may be coated onto artificial or natural carrier fragments or formed thereon in situ. Examples of such carrier fragments are piunice stones, filter stones, aluminum granules and granules of metal alloys such as ferro-silicon, ferro-vanadium, ferro-chrome, and the like, particularly when the surface of the granules has been roughened or etched. Alkalies or alkaline earths may be used as cementing agents, and tend to activate the catalysis.

Example 4 Freshly precipitated aluminum hydroxide containing 10 parts of A1203 are dissolved in a 2N potassium hydroxide solution to form potassium aluminate with a 10 per cent excess of caustic potash. 66 parts of aluminum sulfate plus 18 aq. are dissolved in about 200 parts of water and 17 to 18 parts of cellite brick refuse or other materials rich in silica, such as glaucosil or polysilicates with or without base exchanging powers are stirred in to the aluminum sulfate solution. Examples of excellent polysilicates are those of calcium, copper, iron, zinc, strontium and barium. These polysilicates not only act as diluents but also positively activate and increase the catalytic power of the contact mass for the particular reaction.

The aluminum sulfate suspension is gradually added to the alurninate solution with vigorous agitation until the solution remains strongly alkaline to litmus or preferably neutral or weakly alkaline to phenolphthalein. The reaction product obtained is freed from the mother liquor and dried at a temperature below 100 C., whereupon it is broken into small fragments and constitutes a diluted non-silicious base exchange body.

The reaction product fragments are hydrated by trickling water over them and then part of the exchangeable alkali base is exchanged for a correspond ng amount of calcium oxide or barium oxide in the usual manner using a 5 to 10 per cent solution of the corresponding water soluble salts. After this treatment the base exchange body is impregnated with a chromic acid solution containing 3 to 5 per cent ClOs in order to form the chromate of the diluted base exchange body, which is a salt-like compound and possesses many of the characteristics of a salt, but is of a chemical constitution not yet definitely determined. The particles are then again dried and used directly as contact masses.

Superheated steam is blown through molten phthalic anhydride or derivatives of phthalic anhydride, such as diand tetrachlor phthalic anhydride, at about 190 C., in order to form a gaseous mixture of phthalic anhydride and steam. lhis gaseous mixture is passed over the contact mass described above at 340-450 C., and results in the production of benzoic acid or the corresponding derivatives of benzoic acid containing small amounts of the initial materials as impurities which can be easily separated by the methods described in the preceding example.

Emample 5 Naphthalene vapors mixed with air in the proportion of 1 to 20 are passed over a suitable oxidation catalyst at FIG-420 C. An example of such a catalyst is vanadium pentoxide precipitated on aluminum granules. Phthalic anhydride is produced as an intermediate product in good yield and the phthalic anhydride vapors, associated with the partly deoxygenated air and with steam, are cooled to about 340360 C. with the addition of further superheated steam. This mixture is then passed over a catalyst for splitting off carboxylic groups, thus producing a good yield of benzoic acid from naphthalene in a continuous process.

An example of a good catalyst to be used in this second step is the following:-A mixture of l parts of zinc oxide and 5 parts of aluminum oxide, freshly precipitated. from the corresponding salt solutions by means of 20 per cent ammonia water, are treated with sufficient 2N caustic soda solution to produce a solution of sodium zincate and sodium al 'arninate. 24-30 parts of S102 in the form of an ordinary waterglass solution of 33-36 are diluted with 15-20 volumes of water and -100 parts of cellite brick refuse and glaucosil or colloidal silicic acid are added. The suspension and solution are mixed together with vigorous agitation and warmed to 50430 0., whereupon gradually part of an aluminum zinc zeolite precipitates out. In order to increase the yield of this zeolit-e a 3 to 5 per cent dilute mineral acid such as nitric acid, sulfuric acid or hydrochloric acid is added in a thin stream with vigorous agitation, care being taken that the res."- tion mixture after complete addition of the acid remains alkaline or neutral to phenol phthalein. A gelatinous mass is obtained, which is freed from the mother liquor by pressing, dried at temperatures under 100 C. and then hydrated in the usual manner with 600-1009 parts of water. After hydrating it is treated with a 1 to 2 per cent mineral acid 80111-51011, such as hydrochloric acid or sulfuric acid until substantially all of the exchangeable sodium oxide is dissolved out, producing so-called metallo-silicic acid, which in the present case is a zinc aluminum silicic acid diluted with the materials described above. This body is then dried, and can be directly used for the splitting of the carboxyl group in the process of this example, and gives good results.

Such a contact mass can also be prepared by treating a waterglass solution, containing the diluents as described above, with 5 to 10 per cent solutions of the salts of zinc and aluminum instead of the metallates. For example, nitrates or sulfates may be used, and a zeolite is formed of the aluminum double silicate type which is then subsequently treated as described above and results in a very efiective contact mass. Care should be taken, however, that after adding all of the metal salt solutions to the waterglass suspension the reaction mixture must remain alkaline or neutral to phenolphthalein.

The aluminum and zinc compounds described above may be replaced partly or wholly by compounds of other metals having an amphoteric character, such as for example berylium, cadmium, titanium, zirconium, tin, chromium and particularly lead. These metal compounds may be used singly or in admixture.

The metallo-silicic acids described above may also be pulverized and kneaded with sufiicient soda lime in paste form until the mass can be readily formed into pieces. The amount of soda lime which can be used can be varied within wide limits.

Zeolites which have not been treated with mineral acids to form the metallo-silicic acids may also be used as contact masses in the second step of the process of this example, but in such a case it is desirable to replace part of the exchangeable alkali by calcium, barium or strontium, or by a mixture of these.

Neutral silicates can also be used, particularly when they have been formed under conditions which permit them to remain for a considerable time in the zeolite phase. They may advantageously be diluted with minerals which contain one or more catalytically effective elements.

In the claims the expression polycarboxylic acid substance is used to define and include polycarboxylic acids substituted or unsubstituted and other volatile derivatives which either contain the polycarboxylic acid radical or are capable of yielding polycarboxylic acids by reaction with wa-' ter or steam; examples are esters, (in which the polycarboxylic acid radical is present), anhydrides, (which yield polycarboxylic acids with Water).

What is claimed as new is:

l. A method of producing monocarboxylic acids from polycarboxylic acid substances which comprises vaporizing the polycarboxylic acid substance and passing the vapors of the acid over a contact mass which contains a strong alkali and which favors splitting ofi of carboxyl groups.

2. A method of producing benzoic acids from phthalic anhydrides, which comprises vaporizing the phthalic anhydride and passing its vapors admixed with steam over a catalyst which contains a strong alkali and which favors a splitting off of carboxylic groups.

3. A method of producing benzoic acid from naphthalene, which comprises subjecting the naphthalene to vapor phase catalytic oxidation with an oxygen-containing gas and passing the reaction gases without substantial separation of phthalic anhydride and with an adjustment of the steam content thereof over a contact mass which contains a strong alkali and which favors the splitting oiT of carbon dioxide.

ALPHONS O. JAEGER. 

